1. Field of the Invention
This invention relates to a new process for preparing low molecular weight oxygenated compounds. More particularly, the invention relates to an improved process for preparing low molecular weight oxygenated compounds, and particularly ethylene glycol and methanol, from syngas using a novel catalyst system.
Specifically, the invention provides a new and improved process for preparing low molecular weight oxygenated compounds, and particularly ethylene glycol and methanol, from syngas in good yield, which process comprises contacting a mixture of carbon monoxide and hydrogen with a catalyst system comprising a rhodium-containing compound, an organic ligand and a sulfonium salt, preferably dissolved in a suitable solvent, and heating the resulting mixture at an elevated temperature and pressure for sufficient time to produce the desired low molecular weight oxygenated compounds, and then recovering the same from the reaction mixture.
2. Prior Art
Low molecular weight oxygenated compounds, such as ethylene glycol and methanol, are chemicals which have found wide use in industry. Ethylene glycol, for example, is used in the preparation of plasticizers for vinyl polymers and as a component in polyester fibers and antifreeze formulations. Low molecular weight alcohols, such as methanol, find use as solvents and in the production of esters, such as ethyl esters, which can be subsequently used to produce ethylene. In view of these many uses, there is a need to find new and more economical methods for preparing these chemicals.
One proposed method of making ethylene glycol involves the reaction of carbon monoxide with hydrogen in the presence of variously proposed catalyst systems. In general, the mixture of carbon monoxide and hydrogen, commonly known as synthesis gas or syngas, is reacted at elevated temperatures and pressures in the presence of the proposed catalyst. U.S. Pat. No. 2,636,046 discloses the production of ethylene glycol from syngas using a cobalt catalyst. Belgium Pat. No. 793,086 and U.S. Pat. No. 3,940,432 describe the cosynthesis of ethylene glycol and methanol from mixtures of carbon monoxide and hydrogen using a complex rhodium catalyst. U.S. Pat. No. 3,833,634 describes the use of various other metals as catalysts but indicates that only rhodium and cobalt are effective in producing ethylene glycol. Other patents disclosing catalyst systems for converting syngas into polyhydric alcohols are listed in U.S. Pat. No. 4,162,261.
Many of these proposed processes are limited, however, by the nature and activity of the catalyst systems. For example, many of the catalyst systems have poor selectivity as to the production of the desired polyhydric alcohols, or are based on very expensive components. Other catalyst systems have poor solubility in conventional reaction solvents, or have limited solubility with a plating out of the expensive components, such as rhodium, during the reaction.
It is an object of the invention, therefore, to provide an improved process for preparing low molecular weight oxygenated compounds, and particularly ethylene glycol and methanol. It is a further object to provide a new process for preparing ethylene glycol and methanol from syngas using a new catalyst system. It is a further object to provide a new process for preparing ethylene glycol and methanol from syngas which gives good yields and improved selectivity. It is a further object to provide a new catalyst system from producing ethylene glycol and methanol from syngas which has improved solubility in conventional reaction solvents. It is a further object to provide a new process for preparing ethylene glycol and methanol from syngas which avoids the plating out of expensive components, such as rhodium, during the reaction. Other objects and advantages of the invention will appear hereinafter.